I know the basics of epigenetics, but I do not know how epigenetic mechanisms are transmitted from parents to children (or if there is even enough literature to derive a consensus). My question is relates to surrogate motherhood, in which an egg is fertilized in vitro and then implanted in the womb of a woman other than the egg donor.

Are all the factors that affect epigenetic mechanisms encoded in the genome? Is it possible for the surrogate mother's epigenetics to influence the epigenetics of the child/children?

3 Answers
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Epigenetic information is information that can be inherited through cell division that is not encoded in the DNA sequence. This includes, but is not limited to, DNA methylation and histone modifications (there is also non-chromatin based epigenetic information). A nice example is the centromere, the chromosomal region that binds the kinetochore and is important to attach chromosomes to the mitotic spindle during cell division. The location of the centromere on the chromosome is encoded by a specific nucleosome composition and does not seem to rely on the DNA that wraps around those nucleosomes: The DNA sequence at centromeres is not even conserved from chromosome to chromosome (with the exception of budding yeast), and there are several known examples of people and families where the centromere is in a different place. However, all the mechanisms for maintaining this epigenetic mark are encoded genetically.

As epigenetic information is transmitted through cell division, it is directly inherited from the biological mother (with the exception of e.g. the centromere, most epigenetic marks from the father's chromosomes are removed when sperm is created).

However, (some) epigenetic information can be modified. This is obviously important during development where gene expression patterns of a liver cell need to be stable but different from gene expression patterns of a neuron, even though both descend from the same cell.

There is evidence that the metabolism of the mother will influence the epigenetic program of the child; diet being one of the determinants. It has also been suggested that epigenetic changes may influence behavior. Thus, it is indeed possible for the surrogate mother's epigenetic state to influence the epigenetic information of the children.

The idea of epigentics is that there is more info in chromatin than just in the DNA sequence it contains and that this info can be altered in vivo.
Thus, one cannot inherit epigenetic changes from a surrogate (which brings no new physical genetic material), but the fetus may develop some due to its interactions with her.

The definition of an epigenetic mark I work with is the following :
- impacts gene regulation without touching to the DNA sequence
- is reversible
- is inheritable.

With this definition in mind, you could say that only DNA methylation is a true epigenetic mark, leaving histone modifications and the like to canonical transcription regulation machinery. Yet it really depends on what scale you place yourself. Epigenetics at the scale of the cell is not the same thing as at the scale of the organism.

So if a surrogate mother can alter the epigenetic state of the pup or child or foetus, it will not be due to transmission of information in the traditional sense, but rather be due to her physiological state in the case of the foetus (many hormones act through nuclear receptors that can recruit chromatin remodelers), or as mbq mentioned it, due to her behaviour in the case of the child or pup.

X inactivation is not due to DNA methylation but does impact gene regulation without touching the DNA sequence. Also, the inheritance of the location of the centromere would not fall under your definition, so what kind of mark would that be?
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JonasDec 15 '11 at 17:36

You are totally right, for some reason histone variants did not come to my mind when answering :)
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agrimaldiDec 15 '11 at 18:04